Catalytic domain of the Protein Tyrosine Kinase, C-ros. Protein Tyrosine Kinases (PTK) family; C-ros and Drosophila Sevenless proteins; catalytic (c) domain. The PTKc family is part of a larger superfamily that includes the catalytic domains of other kinases such as protein serine/threonine kinases, RIO kinases, and phosphoinositide 3-kinase (PI3K). PTKs catalyze the transfer of the gamma-phosphoryl group from ATP to tyrosine (tyr) residues in protein substrates. The proto-oncogene c-ros encodes an orphan receptor tyr kinase (RTK) with an unknown ligand. RTKs contain an extracellular ligand-binding domain, a transmembrane region, and an intracellular tyr kinase domain. RTKs are usually activated through ligand binding, which causes dimerization and autophosphorylation of the intracellular tyr kinase catalytic domain. C-ros is expressed in embryonic cells of the kidney, intestine and lung, but disappears soon after birth. It persists only in the adult epididymis. Male mice bearing inactive mutations of c-ros lack the initial segment of the epididymis and are infertile. The Drosophila protein, Sevenless, is required for the specification of the R7 photoreceptor cell during eye development.